I'm a new guy here, so forgive me if I overstep my bounds. But something is fishy about the first round of dynomometer numbers recently posted, and since nobody seemed to pick up the ball and run with it, I figured I'd better dive on the thing.
First, a recap: Greg Vogel at Mossy Nissan has stepped up to the plate with the first cat-back exhaust system for the '02 3.5SE. I think it's darned impressive that anyone with such limited resources could develop and produce a nice-looking exhaust like this one. (The mufflers are too ricey for me, but otherwise the thing looks well screwed together.)
A short time after announcing the system was for sale, Mr. Vogel took an automatic 3.5SE to a local dyno shop and ran the thing with the stock exhaust in place and with his aftermarket unit bolted on. He came up with the following wheel horsepower numbers:
Stock HP peak: 164, no rpm given
Mossy HP peak: 179, no rpm given
Mr. Vogel also ran a 3.5SE with a JWT POPCharger on a dynomometer. He didn't indicate whether this was the same car, the same dynomometer, or even the same day, but he posted the following numbers:
Stock HP peak: 164, no rpm given
POPCharger peak: 174, no rpm given
So what we're looking at is an *extremely* impressive 15 peak horsepower improvement over stock with the Mossy exhaust (and he indicates as many as 20 more horsepower elsewhere on the power curve) and a *very* dynamic 10 horsepower peak gain with the JWT intake. And what we're also seeing is a mathematical quandary of sorts. Nissan advertises 240 SAE crank horsepower for the VQ as installed in this Altima. Including a very conservative number for driveline loss to the front wheels of 20 percent, we should be looking at approximately 192 horsepower on the rollers. Instead, Mr. Vogel reports he's seeing 164, which if the VQ in his test car is making the full complement of 240 horses to the crank indicates a power-sapping driveline loss of 32 percent. Considering the efficiency of today's FWD transaxles, this number flatly does not compute. (In the SE-R community of which I was a member for quite some time, the standard observed driveline loss was in the 15 to 18 percent range.)
So the question is this: Where did all the horses go? Who left the barn door open? Considering the widely tested and reported acceleration numbers for this 3000-pound car, 164 wheel horsepower just ain't gonna get it done. Low- to mid-seven second sprints to 60 miles an hour in SEs with automatic transmissions cannot occur with such low wheel horsepower numbers. And we can certainly be sure that the mid-90 mph trap speeds would be impossible with so much weight and so few horses.
Greg, I'm thinking that your test car is sick. That's the only explanation. I'm also a little leery of those massive horsepower gains you posted. I *really* doubt that the stock exhaust system aft of the catalytic converters is so horribly restrictive that you can free up 15 to 20 horses just by bolting on your exhaust. Heck, 20 wheel horsepower would be an impressive achievement for a full-on set of headers *combined* with a free-flowing exhaust -- we're talking about opening up 25 horsepower at the crank! And the same goes for 10 horses you discovered with the JWT. Bolting on a conical filter and finding twelve or thirteen additional flywheel horsepower is nearly unheard of with relatively small Japanese engines.
Greg, I know that Mossy Nissan doesn't have unlimited pockets for R&D in your parts department, but I'd advise you to run at least two or three other 3.5s -- a mixture of automatics and manuals, if possible -- on the dyno before jumping to the conclusion that these simple bolt-on mods produce such a dramatic horsepower improvement. The sick-looking stock wheel horsepower numbers your test Altima posted should be proof enough of the need for that. (And folks, mods of this type do not produce cumulative horsepower; that is, bolting on both the JWT and the exhaust won't net you a gain of 30 horsepower to the wheels and 38 or so at the crank. Ain't gonna happen. You will not have a 278-horsepower Altima.)
Again, please don't take any of this personally. I'm no engineer. But I do know that when it sounds too good to be true, it very often is.
Jarrod K. Wright
'02 3.5SE 5-speed
'98 SE 5-speed
First, a recap: Greg Vogel at Mossy Nissan has stepped up to the plate with the first cat-back exhaust system for the '02 3.5SE. I think it's darned impressive that anyone with such limited resources could develop and produce a nice-looking exhaust like this one. (The mufflers are too ricey for me, but otherwise the thing looks well screwed together.)
A short time after announcing the system was for sale, Mr. Vogel took an automatic 3.5SE to a local dyno shop and ran the thing with the stock exhaust in place and with his aftermarket unit bolted on. He came up with the following wheel horsepower numbers:
Stock HP peak: 164, no rpm given
Mossy HP peak: 179, no rpm given
Mr. Vogel also ran a 3.5SE with a JWT POPCharger on a dynomometer. He didn't indicate whether this was the same car, the same dynomometer, or even the same day, but he posted the following numbers:
Stock HP peak: 164, no rpm given
POPCharger peak: 174, no rpm given
So what we're looking at is an *extremely* impressive 15 peak horsepower improvement over stock with the Mossy exhaust (and he indicates as many as 20 more horsepower elsewhere on the power curve) and a *very* dynamic 10 horsepower peak gain with the JWT intake. And what we're also seeing is a mathematical quandary of sorts. Nissan advertises 240 SAE crank horsepower for the VQ as installed in this Altima. Including a very conservative number for driveline loss to the front wheels of 20 percent, we should be looking at approximately 192 horsepower on the rollers. Instead, Mr. Vogel reports he's seeing 164, which if the VQ in his test car is making the full complement of 240 horses to the crank indicates a power-sapping driveline loss of 32 percent. Considering the efficiency of today's FWD transaxles, this number flatly does not compute. (In the SE-R community of which I was a member for quite some time, the standard observed driveline loss was in the 15 to 18 percent range.)
So the question is this: Where did all the horses go? Who left the barn door open? Considering the widely tested and reported acceleration numbers for this 3000-pound car, 164 wheel horsepower just ain't gonna get it done. Low- to mid-seven second sprints to 60 miles an hour in SEs with automatic transmissions cannot occur with such low wheel horsepower numbers. And we can certainly be sure that the mid-90 mph trap speeds would be impossible with so much weight and so few horses.
Greg, I'm thinking that your test car is sick. That's the only explanation. I'm also a little leery of those massive horsepower gains you posted. I *really* doubt that the stock exhaust system aft of the catalytic converters is so horribly restrictive that you can free up 15 to 20 horses just by bolting on your exhaust. Heck, 20 wheel horsepower would be an impressive achievement for a full-on set of headers *combined* with a free-flowing exhaust -- we're talking about opening up 25 horsepower at the crank! And the same goes for 10 horses you discovered with the JWT. Bolting on a conical filter and finding twelve or thirteen additional flywheel horsepower is nearly unheard of with relatively small Japanese engines.
Greg, I know that Mossy Nissan doesn't have unlimited pockets for R&D in your parts department, but I'd advise you to run at least two or three other 3.5s -- a mixture of automatics and manuals, if possible -- on the dyno before jumping to the conclusion that these simple bolt-on mods produce such a dramatic horsepower improvement. The sick-looking stock wheel horsepower numbers your test Altima posted should be proof enough of the need for that. (And folks, mods of this type do not produce cumulative horsepower; that is, bolting on both the JWT and the exhaust won't net you a gain of 30 horsepower to the wheels and 38 or so at the crank. Ain't gonna happen. You will not have a 278-horsepower Altima.)
Again, please don't take any of this personally. I'm no engineer. But I do know that when it sounds too good to be true, it very often is.
Jarrod K. Wright
'02 3.5SE 5-speed
'98 SE 5-speed
